Low temperature-calcined TiO₂ for visible light assisted decontamination of 4-nitrophenol and hexavalent chromium...

In the present study, alkaline hydrothermally treated titania nanoparticles (TiO₂-HT) are prepared and followed by calcination at different low temperatures to improve TiO₂ activity under visible light. The prepared photocatalysts (PCs) are characterized by different tools. TiO₂-HT is scrutinized for decontamination of para-nitrophenol (PNP) and hexavalent chromium ions (Cr⁶⁺ ions) under simulated sunlight. TiO₂-HT-300 and TiO₂-HT-400 PCs have nanosized particle with large surface area of 148 and 116.26 m²/g, respectively. Additionally, XRD and FTIR proved formation of nanocrystalline anatase TiO₂. The different calcined TiO₂-HT materials show lower adsorption capacity for PNP and Cr⁶⁺ ions. TiO₂-HT-300 and HT-TiO₂-400 PCs have higher reduction rate of PNP than that of uncalcined temperature titania (HT-TiO₂-U) powder. Complete conversion of PNP is achieved at natural pH after 180 min over TiO₂-HT-300. As well, TiO₂-HT-300 exhibits a superior photocatalytic removal of Cr⁶⁺ ions. The enhanced photocatalytic efficacy is ascribed to the synergism between higher surface area and particle size (quantum effect) of TiO₂-HT-300. As results, HO· radicals are the main key active species for the photocatalytic degradation of PNP over TiO₂- HT-300 PC but contribution of O₂^- and h⁺ holes is minor. The used method for preparation of TiO₂-HT-300 reduces the cost preparation as well as environmental impact reduction. Finally, low temperature-calcined TiO₂ is promising visible light active and an efficient photocatalyst with lower environmental impact for detoxification of PNP and Cr⁶⁺ ions from water.